No abstract

Brazil is the world’s largest sugarcane producer with projections for expanding the current area by 30% in the coming years, mainly in areas previously occupied by pastures. We assess soil water changes induced by land-use change (LUC) for sugarcane expansion in the central-south region of Brazil. For that purpose, soil samples were collected in a typical LUC sequence (native vegetation–pasture–sugarcane) in two contrasting soil textures (i.e., sandy and clayey). Soil hydro-physical properties such as pores size distribution, bulk density, soil water content, water tension, and drainage time at field capacity, plant-available water, and S-index were analyzed. Our data showed that long-term LUC from native vegetation to extensive pasture induced severe degradation in soil physical quality and soil water dynamics. However, conventional tillage used during conversion from pasture to sugarcane did not cause additional degradation on soil structure and soil water dynamics. Over time, sugarcane cultivation slightly impaired soil water and physical conditions, but only in the 10–20 cm layer in both soils. Therefore, we highlight that sustainable management practices to enhance soil physical quality and water dynamics in sugarcane fields are needed to prevent limiting conditions to plant growth and contribute to delivering other ecosystem services.

The use of biochar, which is the solid product of biomass pyrolysis, in agricultural soils, has been shown as a strategic solution for building soil carbon stocks and mitigating greenhouse gas emissions. However, biochar amendment might also benefit other key soil processes and services, such as those that are related to water retention, particularly in sandy soils. Here, we conducted an experiment to investigate the potential of biochar to enhance pore size distribution and water retention properties in a tropical sandy soil. Three biochar rates were incorporated (equivalent to 6.25, 12.5, and 25 Mg ha−1) into plastic pots containing a sandy Oxisol sampled from a sugarcane field in Brazil. Undisturbed samples of the mixture were collected at two evaluation times (50 and 150 days) and used to determine water retention curves and other soil physical properties. The results showed that biochar amendment decreased soil bulk density and increased water retention capacity, micropore volume, and available water content. Higher soil water retention in amended soil is associated with the inherent characteristics of biochar (e.g., internal porosity) and potential improvements in soil structure. Microporosity and water retention were enhanced with intermediate biochar rate (12.5 Mg ha−1), instead of the highest rate (25 Mg ha−1) tested. Further studies are needed to validate these results under field conditions.

Removing sugarcane straw to increase bioenergy production can generate significant income to the industry. However, straw contributes to the regulation of soil functions and consequently supports the provision of ecosystem services, such as water flow regulation. Thus, straw removal may hinder the provision of these services, especially in mechanized sugarcane production systems, which have soil compaction problems due to machinery traffic. In this study, we assess a six-year experiment in Brazil with four rates of straw removal: 0 Mg ha−1 (TR), 5 Mg ha−1 (HR), 10 Mg ha−1 (LR), and 15 Mg ha−1 (NR) remaining straw. Using attributes, such as soil bulk density, porosity, water infiltration, runoff, saturated hydraulic conductivity and available water-holding capacity, as indicators of key soil functions, we calculated a soil-related ecosystem service (ES) index for water flow regulation provision. The ES index revealed that water flow regulation was low regardless of the straw management (0.56, 0.63, 0.64 and 0.60 for TR, HR, LR and NR, respectively). It can be a consequence of soil compaction caused by machinery traffic throughout the successive cycle, whose straw was unable to mitigate this issue. Thus, by the end of the sugarcane cycle (sixth ratoon), straw removal had little effect on soil physical and hydraulic indicators, and consequently had little impact on the provision of the soil-related ES associated with water flow regulation. Nevertheless, straw management should be planned to consider other functions and soil-related ES benefited by straw retention.